The invention relates to pressing machines, particularly household refuse compactors, and still more particularly to the control circuitry employed in such machines.
With known pressing machines of the type in question, it is conventional to connect a direction-reversing relay directly in the current path of the drive motor of the machine. The relay is activated when the motor current and accordingly the motor output torque reach a predetermined value. However, with the known control circuits, the use of the motor-load-dependent direction-reversing relay makes it difficult to modify the pressing force furnished by the machine.
Easy adjustability of the pressing force would be very desirable, whether for the purpose of compensating for undesirable changes in pressing force occuring during operation, or whether for the purpose of taking into consideration the compressibility of the material to be pressed. The latter possibility is particularly meaningful in the case of household refuse compactors, because the refuse being compacted often varies in composition in a known manner. Particularly when vegetables are in season, the refuse will include a high proportion of vegetable material having a high sap or liquid content. It has been shown to be very advantageous to compress refuse of high liquid content only with such force as will not drive out the liquid from the material. Furthermore, for compacting packaging, such as empty tin cans, and for crushing bottles, and the like, a higher compacting force must be utilized. Accordingly, particularly with household refuse compactors, there is the need to be able, in a simple way, to adjust the compacting force supplied by the compactor in consideration of the composition of the refuse to be compacted.
Another problem with pressing machines of the type in question, particularly household refuse compactors, is that of stopping the ram when at the completion of its return stroke it reassumes the starting position. In known machines of this type, use is made of an electric motor and a speed-reducing transmission for moving the compacting ram down onto the refuse to be compacted. When the ram has reached its lowermost or end-of-stroke position the direction of the drive motor is reversed and the ram is lifted back towards the starting position.
In known pressing machines of this type, and especially with household refuse compactors, it is conventional to position an elastic member in the path of return movement of the ram, to cushion and stop the ram and assist in braking by absorbing as potential energy some of the kinetic energy of moving parts of the drive motor and intermediate transmission. However, this way of braking the arrangement has the disadvantage that stresses develop in the transmission, in the linkages connected to the compacting ram, and even in the support framework of the machine. These stresses may even be persistent--i.e., not become relieved even after all moving parts of the machine have come to a complete stop--for example because of friction and self-locking action in the drive and transmission. In order to avoid deformations of parts of the machine, these stresses must be taken into account when designing and dimensioning the parts of the machine. This necessarily leads to an increase in the weight and cost of the machine. But even so, the persisting stresses have an undesirable effect upon the transmission and most of all upon the mounting components.
The stresses developed in this way by the conversion of angular momentum into potential energy during the final coasting of the drive motor and transmission can be avoided by alloting a larger stopping distance for cushioning the ram to a stop, so that the angular momentum of the coasting motor will be dissipated virtually exclusively by the force of friction in the transmission. However, if a larger stopping distance is to be used, then either the total height of the compactor must be made greater or else, if the total height is to be kept unchanged, then there must be a decrease in the useful fraction of the ram stroke. These alternatives are both disadvantageous. If the machine is to be installed in the housing of a box-shaped piece of furniture difficulties arise; if the useful fraction of the ram stroke is to be decreased, then one must accept a marked decrease in the useful capacity of the machine.
Another problem with known pressing machines of the type in question, especially household refuse compactors, involves differences in the composition of the material to be pressed from one pressing operation to the next. For example, when pressing hard material objects, the ram stops suddenly and the inertia of the rotating mass of the rotor and possibly also of its transmission must be dissipated within fractions of a second. This sudden loss of momentum results in the generation of a dynamic (transient) pressing force component which is added to the pressing force component attributable to the output torque of the drive motor. In contrast, when pressing soft or yielding material, the momenton of the moving parts is more gradually dissipated over a longer period of time, as the actual pressing proceeds, so that, when the end-of-stroke activation of the motor-direction-reversing device occurs only the component of pressing force attributable to the motor output torque acts.
This dependence of the pressing force upon the compressibility of the material to be pressed is particularly disadvantageous in the case of household refuse compactors, because with these usually a very inhomogeneous composition of the material to be compacted is involved. Maximum pressing force, attributable to both the motor torque and momentum loss of the moving parts of the pressing machine is produced only when the pressing ram impacts directly upon an unyielding and hard object, for example a bottle, or the like. Only in such event is the pressing ram capable of crushing a bottle or squashing hard objects in the refuse, for example cans and packaging. However, with household refuse, such hard objects are frequently buried within or between soft and yielding material or objects, such as paper, vegetable refuse, or the like. In this event, the relatively low pressing force, resulting from the fact that the pressing ram and accordingly the drive motor are being stopped relatively gradually by the soft and yielding refuse, is insufficient to crush hard objects down to a small volume.
With a household refuse compactor, if it is to be assured that hard objects will be crushed, even if buried within or between soft and yielding material or objects, then it is necessary to increase the pressing force component directly attributable to drive motor output torque to such an extent that this component acting alone is sufficient to accomplish the desired crushing of the hard objects. However, then it must be considered that, in extreme cases, for example when wine bottles or the like are standing upright directly upon the floor of the refuse compartment, the ram may impact very hard upon such objects and come to a relatively violent stop. This results in the superposition of a high dynamic or transient pressing force component upon the already high-dimensioned pressing force component directly attributable to motor output torque. The total of these two strong components will itself be quite high, and this makes disadvantageous demands upon the strength of the machine construction. Accordingly, the machine must be designed on a worst-case basis, which generally involves the cost-increasing use of extra structural material and an undesirable increase of the weight of the machine.